A hydraulic pressure supply- and control-device of this type was exhibited as part of a mobile concrete pump at the trade fair "BAUMA" in April 1992. In this known pressure supply-and control-device, the hydraulic control unit of the distributing boom has control valves which are individually assigned to the pivot drive and the elevation drives of the boom, electro-hydraulically or electro-pneumatically pilot controlled and hydraulically actuated, as well as pressure controlled load-comparative valves which react to the pressures prevailing in the respective partial consumers of the boom, and which are connected to each other in a hydraulic chain and mechanically combined in a control valve block, wherein the valve groups formed by one control valve and one comparative valve, respectively, each of which are assigned to one of the boom drives, are positioned spacially adjacent to each other. Herein, the comparative valves may be serially connected to each other by channels which form sections of a load feedback line. These channels lead from a comparative output of the respective comparative valve to a load-comparative terminal of that adjacent comparative valve which is positioned at the supply device side, as seen from the comparative output of the first valve. These comparative valves are moved into a functional position connecting the load connection to the comparative output and blocking it with respect to the load-comparative input by a relatively higher pressure at a load-connection, at which the pressure effective in the connected partial consumer prevails, than in their load-comparative input, and they are moved into a functional position connecting the load-comparative input to the load-comparative output and blocking this with respect to the load connection by a relatively higher pressure at the load comparative input than at the load-connection. By this, it is attained that the respectively highest pressure prevailing in one of the partial consumers is fed back to the pressure supply device, and that it may be sensed there, in order to adjust the flow rate of the pump of the pressure supply device according to the requirements. The valves combined to form the valve block have disc-shaped casings which have continuous bores in a base arranged in a defined bore layout. These bores are connected communicating each with one supply terminal or one control terminal of the respective valve. Furthermore, the valve casings have continuous bores, through which the tie rods may be stuck by which the valves may be connected to each other, such that the bores communicating with hydraulic terminals of the valves form continuous supply channels which are tightly sealed in the region of the connection planes, at which the casings of adjacent valves lie against each other, with respect to the environment, by O-rings surrounding the ports of the bores.
By this design, a hydraulic longitudinal chain of the valves combined in the block, as viewed in the direction of the casing bores aligned with respect to each other, without an appreciable expenditure of pipes, and an individual layout of the valve block with respect to the design of the mobile concrete pump and the number of moveable arms of the distributing boom, is also possible in a simple way.
A pressure supply- and control -device of this type also has a number of disadvantages, though: The numerous seals resulting from the "sandwich"-design of the valve block have, due to the unavoidable aging of the sealing rings, the consequence that leak oil may exit at the connection points of the valve block at least after some time of use, which is inacceptable even in small amounts. Therefore, the sealing rings have to be exchanged relatively often, which in practice necessitates the removal of the valve block from the vehicle, in order to remove the relatively long tie rods. The same holds for the exchange of defective valves. This maintenance is very time-consuming and expensive with respect to the maintenance and repair expenditures, as well as to the long downtime of the mobile concrete pump itself.